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I'm sorry to hear about the accident...I hope your son wasn't injured. As for coverage, it really depends on the type of policy you have and what your policy says. Usually with comprehensive insurance, the insurance will cover any driver that is operating with permission of the owner/insured. In addition, many policies usually include everyone in the family under the definition of the "insured" party even if they are not specifically named. Comprehensive insurance generally follows the vehicle, not the driver.
Your insurance company should be able to look up your policy and confirm whether permissive drivers are covered by your policy just to ease your mind, but there is a strong likelihood that he will be covered.
Believe it or not, that is pretty much all you have to do. The insurance companies handle these sort of things all the time and will contact you and your son if they need anything else (if they haven't yet, they will be in touch with him to take his statement about what happened and to see if there are any photographs of the damage, etc.). As part of the insurance coverage, provided he is covered, they will represent him through the claims process and through any legal issues, if the other person ends up filing a lawsuit. But insurance companies have adjusters, claims investigators, litigation specialists, and attorneys to handle whatever crops up. The only thing you and your son have to do is make sure you are diligent about cooperating with the insurance company, return all phone calls, etc., since your cooperation is required by your policy.